1. Field of the Invention
This invention concerns concentrated solutions of monosulfonated anthraquinone dyes which retain good solubility even when diluted with hard water. The parent application was examined in Group Art Unit 144.
2. Description of the Prior Art
Monosulfonated anthraquinone dyes generally are somewhat limited in solubility. With the advent of solution dyes for continuous dyeing processes, various methods have been disclosed for preparing 10% to 20% solutions of these dyes for use in said processes. In many cases, lithium and alkanolammonium salts of the dyes were found to be more soluble than sodium salts. In most cases, the aqueous solutions employ a supplementary water-miscible solvent of fairly low molecular weight.
A failing of solutions of monosulfonated anthraquinone dyes is a tendency to precipitate calcium or magnesium salt forms of the dyes when water containing these ions is added to the dye solutions. Another failing of these solutions is a tendency to precipitate the dye when pH of the solution is lowered to about 4.0 or below. This precipitation is particularly objectionable when the dye comes out of solution in a gel form which is very difficult to remove from transfer lines.
What is needed is a solution to the problem of anthraquinone dye gelation in order to eliminate plugging and contamination of transfer lines. The following courses of action which can be gleaned from the prior art are not satisfactory: (1) use of triethanolamine as a dye solubilizer, (2) use of the sodium salt of ethylenediaminetetraacetic acid (EDTA) as a chelating agent, (3) use of triethanolamine together with the commonly used sodium salt of ethylenediaminetetraacetic acid (EDTA).
Relevant prior art includes the following. The anthraquinone dyes, "Acid Blue 40", Colour Index No. 62125, and "Acid Blue 25", Colour Index No. 62055, are disclosed in U.S. Pat. No. 1,131,516.
U.S. Pat. No. 3,055,726 discloses the use of the sodium salt of ethylenediaminetetraacetic acid and a polymeric alkali metal phosphate in a dye bath containing hard water and sodium carbonate. Summersgill, Journal of the Society of Dyers and Colourists 70, 278-283 (1953), discloses that some recalcitrant wool dyes can be prevented from precipitating in hard water by adding ethylenediaminetetraacetic acid. The only specific dye mentioned in this article is a disulfonated azo dye.
The Dow Chemical Company's Versene literature recommends use of triethanolamine with the tetrasodium salt of ethylenediaminetetraacetic acid in systems containing ferric ion in alkaline systems. U.S. Pat. No. 2,992,064 discloses use of the triethanolamine salt of ethylenediaminetetraacetic acid to treat dyed fabrics for the purpose of inhibiting gas fading. U.S. Pat. Nos. 2,314,356 and 3,681,320 disclose alkanolammonium salts as offering improved dye solubilities.